Zoom lens barrel including a mechanism for moving lens groups

ABSTRACT

A zoom lens barrel in which a zoom lens is switched to a plurality of focal lengths by a moving member by which a plurality of lens groups are moved in the direction of optical axis. After a desired focal length has been selected, a focusing operation is conducted by the moving member. At least two lens groups, which are moved for switching focal lengths, are moved while a distance between lens groups is being changed so that the focusing operation can be conducted.

This is a division of application Ser. No. 08/226,562, which is now U.S.Pat. No. 5,668,670, filed Apr. 12, 1994.

BACKGROUND OF THE INVENTION

The present invention relates to a compact zoom lens barrel.

A conventional zoom lens barrel comprises a zoom system, by which onefocal length is switched to another focal length, and a focusing drivingsystem, by which focusing is conducted. In conventional zoom lensbarrels, several system, in which zooming and focusing are linkedtogether, have been proposed.

For example, in Japanese Patent Publication Open to Public InspectionNo. 287833/1988, and No. 248110/1991, the following has been proposed: afocal length switching cam portion and a focusing cam portion are linkedtogether, and form one driving system; focal length switching andfocusing are conducted by this one driving system, and a subsidiaryoptical system is not necessary. In these publications, a zooming regionis divided into a focal length switching region and focusing region; afocal length is selected stepwise; when a parallel cam portion, which isnot moved in the direction of an optical axis at the time of focusing,is provided, a lens group other than a focusing lens group is used forfocal length switching and focusing; and a lens barrel is made to besmall and the cost is lowered. In Japanese Patent Publication Open toPublic Inspection No. 259210/1986, a whole lens system is protruded atthe time of focusing, however, disadvantageous points, which will bedescribed later, occur in the whole lens system protrusion.

In these conventional technologies, the effect of thinning the lensbarrel is small, and when a zoom lens, in which sensitivity for errorsin distance between lens groups (which will be described in detaillater) is high, is used for focusing by the zoom lens barrel, there aremany disadvantageous points to be solved, such as focusing accuracy.Further, focusing operations of respective lenses have not beendisclosed.

Presently, a zoom type compact camera advances in the direction ofdown-sizing and thinning of the camera body, however there are manyobstacles to this advancement. First of these is dimensions of the zoomlens. When too much thinning is attempted, an fb (flange back) becomestoo short, an aperture of the final lens, which is closest to a filmsurface, becomes large, and a switching mechanism for panoramaphotographing can not be housed in the camera body. Further, when theaperture of the final lens becomes large, the diameter of the lensbarrel becomes too large, so that the camera body itself tends to becomelarger. Due to the foregoing, the present inclination is as follows:when the total length of the lens is kept to a certain value, and thelens barrel is constructed in the manner of double-structure, the amountin which the lens can be driven is kept constant and the length of thelens barrel is shortened.

However, the diameter of the double-structured lens barrel is large, andalthough the effect of thinning the lens barrel is high, the effect islow for a decrease of the diameter of the lens barrel. Accordingly, inorder to decrease the diameter of the lens barrel, the structure of acam cylinder+a cam pin+a helicoid is changed to a structure of a doublehelicoid+an inner cam.

This is structured as follows: a front lens group portion is linearlydriven through a helicoid of the cam cylinder which is rotated by a lensbarrel driving motor; and a rear lens group portion is driven by aninner cam provided inside the cam cylinder. Since the cam portion is notexposed on the external visible surface, the diameter of the lens barrelcan be made small since the cam cylinder can also be used for anexternal visible part, and it is not necessary to provide a separatedriving gear to the metallic cam.

However, the diameter of the front lens group portion, in which afocusing mechanism is housed, is still large. When a 6V battery ischanged to a 3V battery in order to make the camera more compact, afocusing motor and the like can be enlarged in order to obtain a higheroutput power.

Further, in the zoom lens, an FC adjustment in which both a telescopiclens and a wide lens focus on the same plane, and an ff adjustment, inwhich both lenses, having focused on the same plane, focus on a focalplane, are conducted. In the FC adjustment, a space for adjustment isnecessary between a diaphragm and the front lens group, and positions ofthe diaphragm and lenses are changed depending on the adjustment, whichleads to problems, causing the diameter of the front lens group portionto be large. In the ff adjustment, it is necessary that the whole lensbarrel is moved, and it is necessary that large parts, which areappropriately strong for supporting the movement of the lens barrel, areprovided on the lens barrel, so that the diameter of the lens barrelbecomes larger.

The number of lenses is decreased at the sacrifice of the brightness(F-number) of the photographic lens, and the dimensions of the lensbarrel is made to be compact, accompanied with requirements forcompactness and low cost of the lens barrel. Accordingly, lensperformance and the like are necessarily deteriorated. Part members ofthe lens barrel are made of plastic. Accordingly, the focusingperformance, and resolving performance are necessarily sacrificed due tothe dimensional accuracy, deformation, and the like. As described above,the structure of compact zoom-lens cameras has been changed many timesfor the purpose of compactness and low cost. However, the compactnesshas almost reached its limit, and lower cost can not be achieved withoutsacrificing specifications and performance.

SUMMARY OF THE INVENTION

The above-mentioned problems can be overcome by a zoom lens barrelaccording to the present invention, in which the zoom lens barrel ischaracterized in that: a zoom lens is switched to a plurality of focallengths by a moving means by which a plurality of lens groups are movedin the direction of optical axis; after a desired focal length has beenselected, a focusing operation is conducted by the moving means; atleast two lens groups, which are moved for switching focal lengths, aremoved while a distance between lens groups is being changed so that thefocusing operation can be conducted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a zoom lens barrel accordingto the present invention.

FIG. 2 is a horizontal sectional view of the zoom lens barrel.

FIGS. 3A and 3B are an illustration of an assembly of a fixed plate.

FIG. 4 is a diagram of a step zooming operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Initially, characteristics of the present invention and advantageousfeatures, which are compared with the prior art, will be explainedlogically and interspersing with simulation data. Next, embodiments ofspecific structures will be explained while referring to the drawings.

An object of the present invention is to increase compactness and lowercost of the zoom lens barrel for a compact camera, and simultaneously toimprove the focusing performance, focusing operation and lensperformance. When a cam portion for switching focal lengths and a camportion for focusing are sequentially provided in the zoom lens barrel,a focal length switching driving means and a focusing driving means canbe included in one driving means. When at least two lens groups, whichare used for varying the magnification at the time of focusing, aremoved while a distance between the lenses is being changed, influencesof the accuracy of a focusing stop on the accuracy of the focal positionare decreased, focusing control can be conducted with higher resolution,the zoom lens barrel can be compact by adoption of a high errorsensitivity lens, a focal position adjustment mechanism is simplified,the lens performance can be made higher by improvement, and the zoomlens barrel can be more compact and cost less.

To move at least two lens groups at the time of focusing in order toswitch a focal length will be called "twin focus" hereinafter. Further,in a lens barrel in which a focal length switching operation and afocusing operation are conducted by a single driving motor, a mechanism,by which the focal length switching operation and the focusing operationare selected in specific increments, will be called a "step zoom"hereinafter.

A decrease of influences for improving the resolving power of focusingcontrol and an error of a stopping position on the accuracy of a focalposition!

The error sensitivity of a zoom lens will be described below. In thezoom lens in which two lens groups composed of a first lens group (FClens) and a second lens group (RC lens) are moved, a change of lenspositions does not necessarily coincide with a change of a focalposition. For example, when only a front lens of the lens having errorsensitivity of 8 times is moved 1 mm under the telescopic conditions,the focal position is moved 8 mm. This is called error sensitivity indistance between FC and RC, or error sensitivity in distance betweenlens groups, and shows the difficulty in which high focusing performanceis achieved in a zoom lens. (hereinafter, called error sensitivity).

In the case of 2 group zooming, the error sensitivity is expressed bythe following equation.

    G=Δfb/Δd=(f/f1).sup.2                          1

Where,

G: error sensitivity

Δd: a moving amount of the lens distance

Δfb: an amount of a change of a focal position

f1: a focal length of the first lens group (FC group)

f: a synthetic focal length (a focal length of the zoom lens system)

That is, the error sensitivity has a larger value as the focal length ofthe first lens group is shorter, or the synthetic focal length islarger.

The synthetic focal length is expressed by the following equations:

    1/f=(1/f1)+(1/f2)-{H/(f1·f2)}                     2

Where,

H: a distance between principal points of the first lens group and thesecond lens group

f1: a focal length of the first lens group (FC group)

f2: a focal length of the second lens group (RC group)

When the focal length of an FC lens (+) is enlarged, the synthetic focallength becomes larger. When the focal length of an RC lens (-) isenlarged, the synthetic focal length becomes shorter, and when adistance between lenses is enlarged, the synthetic focal length becomesshorter.

For example, in the case where the required accuracy for focusing is±0.15, when the sensitivity for the error is supposed to be 7.5, thesensitivity for the error can not be achieved without decreasing thedistance between lenses to less than ±0.02. The reason for increasingthe sensitivity for the error is for the purpose of down-sizing the zoomlens barrel. When the focal length can be changed with a small amount oflens protrusion, the lens barrel can be made smaller. Even whencompactness of the lens barrel is not required, the sensitivity forerrors is necessary to some extent in order to prevent the lens barrelfrom being enlarged, and to ensure the lens performance. The sensitivityfor errors, the value of which is about 6 to 9, is adopted in many casesin the case of a 2 power telephoto type zoom lens barrel, the focallength of which is 35 to 70 mm.

As an example, in a two-group zoom lens, in which the focal length ofthe first lens group is 24.5 mm, and the focal length of the second lensgroup is -22.5 mm, the distance between principal points of the firstand the second lens groups is 17.28 mm in a wide lens (f=36.0 mm), and10.03 mm in a telescopic lens (f=68.5 mm), the sensitivity for errors is2.15 in the wide lens, and 7.72 in the telescopic lens from equations 1and 2.

Although the movement amount of the front lens in a front lens focusingtype lens is approximately 1.2 mm in the case of a finite distance 0.6m, this movement amount is only 5.28% of the 22.72 mm movement of thezoom lens (the movement of the FC lens from wide∞to tele∞). When thisfocusing region is divided into 100 increments (100 steps) for thepurpose of auto-focusing, the movement ratio of the front lens is 0.053%for each step. In the auto-focusing control by the drive of the zoomlens barrel in a mechanism, which is used for focusing and also forswitching the focal length, a minute movement amount is controlled withrespect to the total zooming amount. In order to control this minutemovement amount and to use the lens, in which the sensitivity for errorsis high, the allowable amount for backlash and deformation of the lensbarrel is drastically reduced, and also the allowable amount for arotation angle error at the time of control for the lens barrel stop, isreduced.

When the rotation angle of the cam barrel is enlarged in order toenlarge the focusing region, this minute amount is made larger. However,the focal length switching region is also enlarged, and the movementtime for switching the focal length is also increased. Here, when a gearratio of the driving system is changed, there is the possibility thatsatisfactory torque can not be obtained. Further, when the focal lengthis switched by a high voltage, and a focusing operation is conducted bya low voltage, the timed relationship can be well balanced. However,these operations can not be conducted when the capacity of the powersupply is not adequate, and the driving circuit becomes complex, whichleads to excessive overall cost. In any case, the relationship betweenthe focal length switching operation and the focusing operation in amechanical region is not changed.

Accordingly, it is desired that the focusing region is enlarged by amethod which does not affect focal length switching. When the spreadamount of the lens distance, generated at the time of focal lengthswitching, is reduced, the movement amount of the front lens can beincreased. Accordingly, when the RC lens is moved in the direction ofthe FC lens movement at a predetermined ratio, since the spread amountof the lens distance between the FC and RC lenses is decreased withrespect to the movement amount of the FC lens, the movement amount ofthe FC lens can be increased. For example, when the RC lens is moved byabout half of the movement amount of the FC lens, the movement amount ofthe FC lens is 1.2 mm in the case of a front lens protrusion type, andis approximately 2.1 mm in the case of twin-focusing. The resolvingpower is improved by 77%, and the sensitivity for errors of the lensbarrel stop is decreased by the improved amount of the resolving power.When a lens having a higher sensitivity for errors is used by utilizingthis decrease of the sensitivity for errors of the lens barrel stop, thewhole lens barrel can be made smaller.

When the error of front lens focusing is compared with that of twinfocusing of 2:1, in the lens in which the sensitivity for errors is7.79, the changed amount of fb at the time when the FC lens is moved by0.1 mm, is as follows.

    ______________________________________                                        Front lens focusing   0.779 mm                                                Twin focusing         0.440 mm                                                ______________________________________                                    

The amount of the fb of twin focusing is changed by only 56% of theamount of the fb in front lens focusing.

An movement amount of the focusing position is calculated by thefollowing equation.

    Δfb=(FC.sub.S -RC.sub.S)×G+RC.sub.S

Where,

Δfb: the movement amount of focusing position

FC_(S) : the movement amount of the FC lens

RC_(S) : the movement amount of the RC lens

G: the sensitivity for errors

In this case, where the movement amount of the RC lens is the same asthat of the FC lens, the case corresponds to the whole lens barrelprotrusion, and is not affected by the sensitivity for errors.

The following can be found: when the RC lens, other than the FC lens, ismoved at the time of focusing, the movement amount of the FC lens isincreased; and the influence on the error of the focal position isdecreased with respect to the error of the rotation angle at the time ofthe control of the lens barrel stop. Accordingly, when twin focusing isconducted, the ratio of the region of focal length switching to theregion of focusing can be changed; the influence due to the error at thetime of control of the lens barrel stop can be decreased; and theresolving power for the control can be changed. When the RC lens ismoved in the reverse direction to the FC lens, effects opposite to theforegoing can be expected. When the RC lens is moved in the samedirection as the FC lens, and the movement amount of the RC lens islarger than that of the FC lens, the total movement amount, which islarger than that of the whole lens barrel protrusion type, can beobtained. When (Δfb is in the range of "+") or the movement ratio of theFC and RC lenses is changed between a wide range and a telescopic range,lens design, in which an amount of the focusing control (the rotationangle of the cam barrel) is made to be constant, can be conducted.

Simplification of the focal position adjustment and a mechanism thereof!

Next, a focal position adjustment method will be described. In aconventional zoom lens, focal lengths are continuously provided in thewhole range. Accordingly, when only the lens position of one lens groupis simply adjusted, focusing on the whole range can not be conducted.Therefore, two lens position adjustment, that is, FC adjustment and ffadjustment are necessary. The FC adjustment is adjustment by which thefocal position is adjusted in the same plane in both the telescopicrange and the wide range, and generally, the FC adjustment is conductedwhen the FC lens is moved forward and/or backward.

(Adjustment of the distance between lens groups)

Next, the ff adjustment, by which the whole lens groups are moved, isconducted so that the lens, which has been focused in the same plane, isfocused on the focal plane of the camera. For example, when the focalposition of a wide lens is deviated by 0.4 mm in the forward direction,and the focal position of a telescopic lens is deviated by 1.4 mm in thebackward direction under the conditions that the lens has been justassembled, the sufficient focusing operation of the wide lens and thetelescopic lens can be conducted when the distance between lenses isenlarged by 0.3 mm, and the whole lens position is moved backward by 1.0mm (in the case where the sensitivity for errors of the wide lens is 2:and that of the telescopic lens is 8).

However, it is a very rare case that the lens can focus on the focalplane in the whole range of the lens by this method. This adjustmentmethod is suitable for only in a case where ideal FC, RC lenses and camsare provided. In many cases, good focusing can not be obtained in themiddle range. In such a case, since the reason for non focusing is notdue to only the distance between the RC and FC lenses and thesepositions, suitable focusing can not be obtained by only the adjustmentof the lens distance and the movement of the whole lenses. In manycases, it is difficult to obtain good focusing in the central range ofthe zoom lens due to dimensional errors of cams or mechanical portions,and errors of the lens system.

Recently, it has been proposed that the continuous focal length iscontrolled stepwise, and the movement amount of the focusing lens iscorrected for each focal length which is obtained stepwise (by softwareusing an EEP-ROM). Accordingly, it is solved that the focusingperformance is deteriorated at the center of the zoom lens. The presentinvention is a typical example in which the focal length is controlledstepwise, and the focusing performance is improved by using the softwaretechnology.

The present invention is accomplished when the cam inclination forprotrusion of the FC and RC lenses which are moved at the time offocusing, is kept constant; and when the ∞ side and the closest side ofa horizontal cam are extended. The focal position is adjusted accordingto the protrusion characteristics for each focal length which can beselected stepwise. This adjustment is called twin-focusing adjustment.That is, the focal position adjustment is conducted by only the rotationangle adjustment of the cam barrel, and the adjustment of the distancebetween lens groups and the whole position adjustment are not conducted.In other words, when an amount of focusing is changed, the focalposition adjustment is conducted. This operation is the same as that ofa single focus lens camera, and in this case it is conducted for eachfocal length. As compared with the conventional operations in which thefocal position is checked, adjusted and corrected in both the telescopicrange and the wide range, the adjusting operation is greatly simplified.An EEP-ROM is used for storing this individual difference for each focallength.

Here, the focal length error of the twin-focus type focal positionadjustment is simulated as follows. Conditions of the simulation are asfollows.

Sensitivity for error of distance between lens groups!

When the FC lens group is moved forward,

    ______________________________________                                        wide (M)              2.16 times                                              middle (M2)           4.47 times                                              telescopic (T)        7.79 times                                              ______________________________________                                    

Focal length error!

When the error of the distance between lens groups is +0.1 mm,

    ______________________________________                                               wide          -0.6402%                                                        middle        -0.9673%                                                        telescopic    -1.2044%                                                 ______________________________________                                    

The calculation equation for FC, ff adjustments of the conventionalzoom!

An FC adjustment amount=(ΔfbW-ΔfbT)/(GT-GW)

An ff adjustment=-ΔfbW-(FC adjustment amount×GW)=-ΔfbT-(FC adjustmentamount×GT)

Where,

GW: the sensitivity for error in the wide range

GT: the sensitivity for error in the telescopic range

ΔfbW: the deviation amount of focusing in the wide range

ΔfbT: the deviation amount of focusing in the telescopic range

A twin-focus ratio!

    FC.sub.S :RC.sub.S =2:1

A focusing correction amount of the twin-focus!

the sensitivity for error is defined as G, and from equation 3,

Δfb=correction Ad×G+correction Δd

correction Δd=Δfb/(G+1)

correction in the wide range Δd=Δfb/3.16

correction in the middle range Δd=Δfb/5.74

correction in the telescopic range Δd=Δfb/8.79

Where,

Δfb: an error of the focal position,

Δd : the distance between lenses,

ΔFC: the deviation amount of the distance between lenses beforeadjustment,

Δff: the deviation amount of the whole lens before adjustment

For simplification, it is assumed that the FC lens and RC lens have noerror.

1. When the focal position adjustment is conducted on a lens unit whichhas an error of 0.1 mm in the forward direction in only the FC lensgroup (ΔFC=0.1 mm),

    ______________________________________                                        Before the adjustment                                                                        W         M2        T                                          Δfb      0.216 mm  0.474 mm  0.779 mm                                   The focal length                                                                             -0.640%   -0.967%   -1.204%                                    ______________________________________                                    

In a conventional case:

since the focal position is perfectly corrected by the adjustment of thedistance between lenses, there is no error in the focal length. (FCadjustment)

    ______________________________________                                        Error Δd    0 mm     0 mm     0 mm                                      Error of the focal length                                                                       0%       0%       0%                                        Δfb after the adjustment                                                                  0 mm     0 mm     0 mm                                      ______________________________________                                    

When the FC adjustment is conducted for each focal length:

same as the conventional case

When the ff adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             0.1 mm     0.1 mm     0.1 mm                                     Error of the focal length                                                                  -0.640%    -0.967%    -1.204%                                    Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       In the present invention:                                                                  W          M2         T                                          Correction Δd                                                                        -0.068 mm  -0.083 mm  -0.089 mm                                  Error Δd                                                                              0.032 mm   0.017 mm   0 011 mm                                  Error of the focal length                                                                  -0.203%    -0.169%    -0.137%                                    Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

2. The focal position adjustment is conducted on a lens unit in whichthe whole lens groups has an error of 0.1 mm in the forward direction.(Δff=0.1 mm)

    ______________________________________                                        Before adjustment                                                                            W         M2        T                                          Δfb      0.1 mm    0.1 mm    0.1 mm                                     Error of the focal length                                                                    0%        0%        0%                                         ______________________________________                                    

In a conventional case:

since the focal position is perfectly corrected by the adjustment of thewhole lens groups, there is no error in the focal length. (ffadjustment)

    ______________________________________                                        Error Δd    0 mm     0 mm     0 mm                                      Error of the focal length                                                                       0%       0%       0%                                        Δfb after the adjustment                                                                  0 mm     0 mm     0 mm                                      ______________________________________                                    

In the case where the FC adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             -0.0460 mm -0.021 mm  -0.013 mm                                  Error of the focal length                                                                  0.296%     0 204%     0 155%                                     Δfb after adjustment                                                                 0 mm       0 mm       0 mm                                       ______________________________________                                    

In the case where an ff adjustment is conducted for each focal length:

Same as the conventional case.

    ______________________________________                                        In the present invention:                                                                  W          M2         T                                          correction Δd                                                                        -0.032 mm  -0.017 mm  -0.011 mm                                  Error Δd                                                                             -0.032 mm  -0.017 mm  -0.011 mm                                  Error of the focal length                                                                  0.203%     0.169%     0.137%                                     Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

3. The focal position adjustment is conducted on a lens unit, in whichthe FC lens group has an error of 0.1 mm in the forward direction, onlyat the wide end.

    ______________________________________                                        Before adjustment:                                                                         W          M2         T                                          Δfb    0.216 mm   0. mm      0.mm                                       Error of the focal length                                                                  -0 640%    0%         0%                                         In the conventional case:                                                     an FC adjustment amount                                                                       0.0384 mm                                                     an ff adjustment amount                                                                      -0.2989 mm                                                     Error Δd                                                                             0.138 mm   0.038 mm   0.038 mm                                   Error of the focal length                                                                  -0.886%    -0.371%    -0.462%                                    Δfb after the adjustment                                                             0 mm       -0.117 mm  0 mm                                       ______________________________________                                    

In the case where the FC adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd    0 mm     0 mm     0 mm                                      Error of the focal length                                                                       0%       0%       0%                                        Δfb after the adjustment                                                                  0 mm     0 mm     0 mm                                      ______________________________________                                    

In the case where the ff adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             0.1 mm     0 mm       0 mm                                       Error of the focal length                                                                  -0.640%    0%         0%                                         Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       In the present invention:                                                                  W          M2         T                                          correction Δd                                                                        -0.068 mm  0 mm       0 mm                                       Error Δd                                                                              0.032 mm  0 mm       0 mm                                       Error of the focal length                                                                  -0.203%    0%         0%                                         Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

4. The focal position adjustment is conducted on a lens unit in whichthe FC lens group has an error of 0.1 mm in the forward direction, onlyat the telescopic angle end.

    ______________________________________                                        Before adjustment                                                                          W          M2         T                                          Δfb    0 mm       0.mm       0.779.mm                                   Error of the focal length                                                                  0%         0%         1.204%                                     In the conventional case:                                                     an FC adjustment amount                                                                      -0.1384 mm                                                     an ff adjustment amount                                                                       0.2989 mm                                                     Error Δd                                                                             -0.138 mm  -0.138 mm  0.038 mm                                   Error of the focal length                                                                  0.886%     1.338%     0.462%                                     Δfb after the adjustment                                                             0 mm       -0.357 mm  0 mm                                       ______________________________________                                    

In the case where the FC adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd    0 mm     0 mm     0 mm                                      Error of the focal length                                                                       0%       0%       0%                                        Δfb after the adjustment                                                                  0 mm     0 mm     0 mm                                      ______________________________________                                    

In the case where the ff adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             0. mm      0 mm       0.1 mm                                     Error of the focal length                                                                  0%         0%         -1.2040%                                   Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       In the present invention:                                                                  W          M2         T                                          Correction Δd                                                                        0 mm       0 mm       -0.089 mm                                  Error Δd                                                                             0 mm       0 mm        0 011 mm                                  Error of the focal length                                                                  0%         0%         -0.137%                                    Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

5. The focal position adjustment is conducted on a lens unit, in whichthe FC lens group has an error of 0.1 mm in the forward direction, onlyat the wide angle end.

    ______________________________________                                        Before adjustment:                                                                         W          M2         T                                          Δfb    0.1 mm     0.mm       0.mm                                       Error of the focal length                                                                  0%         0%         0%                                         In the conventional case:                                                     an FC adjustment amount                                                                       0.0178 mm                                                     an ff adjustment amount                                                                      -0.1384 mm                                                     Error Δd                                                                             0.018 mm   0.018 mm   0.018 mm                                   Error of the focal length                                                                  -0.114%    -0.172%    -0.214%                                    Δfb after the adjustment                                                             0 mm       -0.054 mm  0 mm                                       ______________________________________                                    

In the case where the FC adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             -0.048 0 mm                                                                              0 mm       0 mm                                       Error of the focal length                                                                  0.2960%    0%         0%                                         Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

In the case where the ff adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             0 mm       0 mm       0 mm                                       Error of the focal length                                                                  0%         0%         0%                                         Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       In the present invention:                                                                  W          M2         T                                          Correction Δd                                                                        -0.032 mm  0 mm       0 mm                                       Error Δd                                                                             -0.032 mm  0 mm       0 mm                                       Error of the focal length                                                                  0.203%     0%         0%                                         Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

6. The focal position adjustment is conducted on a lens unit in whichthe FC lens group has an error of 0.1 mm in the forward direction, onlyat the telescopic angle end.

    ______________________________________                                        Before adjustment:                                                                         W          M2         T                                          Δfb    0 mm       0.mm       0.1 mm                                     Error of the focal length                                                                  0%         0%         0%                                         In the conventional case:                                                     an FC adjustment amount                                                                      -0.0178 mm                                                     an ff adjustment amount                                                                       0.0384 mm                                                     Error Δd                                                                             -0.018 mm  -0.018 mm  -0.018 mm                                  Error of the focal length                                                                  0.114%     0.172%     0.214%                                     Δfb after the adjustment                                                             0 mm       -0.046 mm  0 mm                                       ______________________________________                                    

In the case where the FC adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             0 mm       0 mm       -0 013 mm                                  Error of the focal length                                                                  0%         0%         0 155%                                     Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

In the case where the ff adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             0. mm      0 mm       0 mm                                       Error of the focal length                                                                  -0.640%    0%         0%                                         Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       In the present invention:                                                                  W          M2         T                                          Correction Δd                                                                        0 mm       0 mm       -0.011 mm                                  Error Δd                                                                             0 mm       0 mm       -0 011 mm                                  Error of the focal length                                                                  0%         0%         0.137%                                     Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

7. In the case where the focal position adjustment is conducted on aunit in which the whole lens groups have an error of 0.1 mm in theforward direction under the condition that the FC lens group has anerror of 0.1 mm in the forward direction:

    (ΔFC=0.1 mm, Δff=0.1 mm)

    ______________________________________                                        Before adjustment                                                                          W          M2         T                                          Δfb    0.316 mm   0.574 mm   0.879 mm                                   Error of the focal length                                                                  -0.640%    -0.9670%   -1.204%                                    ______________________________________                                    

In the conventional case:

the focal position adjustment amount is perfectly corrected with an FCadjustment amount of -0.1 mm, and an ff adjustment amount of -0.1 mm.(FC adjustment, ff adjustment)

    ______________________________________                                        Error Δd    0 mm     0 mm     0 mm                                      Error of the focal length                                                                       0%       0%       0%                                        Δfb after the adjustment                                                                  0 mm     0 mm     0 mm                                      ______________________________________                                    

In the case where the FC adjustment is conducted for each focal length:

    ______________________________________                                        Correction Δd                                                                        -0.146 mm  -0.121 mm  -0.113 mm                                  Error Δd                                                                             -0.046 mm  -0.0210 mm -0.013 mm                                  Error of the focal length                                                                  0.296%     0.204%     0 155%                                     Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

In the case where the ff adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             0.1 mm     0.1 mm     0.1 mm                                     Error of the focal length                                                                  -0.640%    -0.967%    -1.204%                                    Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       In the present invention:                                                                  W          M2         T                                          Correction Δd                                                                        -0.1 mm    -0.1 mm    -0.1 mm                                    Error Δd                                                                             0 mm       0 mm       0 mm                                       Error of the focal length                                                                  0%         0%         0%                                         Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

8. In the case where the focal position adjustment is conducted on aunit in which the whole lens groups have an error of 0.1 mm in theforward direction under the condition that the FC lens group has anerror of 0.1 mm in the forward direction only at the telescopic end:

    (ΔFC at the telescopic end=0.1 mm, Δff=0.1 mm)

    ______________________________________                                        Before adjustment:                                                                           W         M2        T                                          Δfb      0.1 mm    0.1 mm    0.879 mm                                   Error of the focal length                                                                    0%        0%        1.204%                                     In the conventional case:                                                     an FC adjustment amount:                                                                     -0.1384 mm                                                     an ff adjustment amount:                                                                      0.1989 mm.                                                    Error Δd -0.138 mm -0.138 mm -0.038 mm                                  Error of the focal length                                                                    0 886%    1.388%    0.462%                                     Δfb after the adjustment                                                               0 mm      -0.357 mm 0 mm                                       ______________________________________                                    

In the case where the FC adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             -0.046 mm  -0.021 mm  -0.013 mm                                  Error of the focal length                                                                  0.296%     0.204%     0.155%                                     Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

In the case where the ff adjustment is conducted for each focal length:

    ______________________________________                                        Error Δd                                                                             0 mm       0 mm       0.1 mm                                     Error of the focal length                                                                  0%         0%         -1.204%                                    Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       In the present invention:                                                                  W          M2         T                                          Correction Δd                                                                        -0.032 mm  -0.017 mm  -0.1 mm                                    Error Δd                                                                             -0.032 mm  -0.017 mm  0 mm                                       Error of the focal length                                                                  0.203%     0.169%     0%                                         Δfb after the adjustment                                                             0 mm       0 mm       0 mm                                       ______________________________________                                    

In the foregoing conventional method, errors of the lens distance andthe position of the whole lens groups can be accurately corrected.However, in the case where there are errors in the zoom lens due to camsor the like, sufficient focusing can not be obtained in the center rangeof the zoom lens, and further, when the focusing operation is conducted,the error of the focal length is increased. (Examples 3, 4, 5, 6, and 8)

These errors are improved when focal position adjustment is conductedfor each focal length. When an ff adjustment is conducted for each focallength, the adjustment amount in the telescopic range is large, theerror of the focal length due to the error of the distance between thelenses is not improved. In a mechanical view, it is difficult that theff adjustment is conducted for each focal length. (Examples 1, 3, 4, 7and 8)

When the FC adjustment is conducted for each focal length, the error isdecreased, compared to the ff adjustment. However, when errors exist inthe whole lens groups at the wide angle range, the errors can besignificant, so that improvement is necessary. (Examples 2, 5, 6, 7 and8).

Due to the foregoing, the FC adjustment is advantageous in thetelescopic range, but the positional errors of the whole lens groupsremain in the wide angle range when only FC adjustment is conducted.

The twin-focus type lens adjustment method can have an effect of the FCadjustment and the effect of the ff adjustment. This method is moreimproved than the FC adjustment method simply in absorption of thepositional errors of the whole lens groups. This can be confirmed by thefollowing equation.

    FC adjustment: Δd=Δfb/G

    Twin-focus adjustment: Δd=Δfb/(G+1)

    (Twin-focus ratio FD.sub.S : RC.sub.S =2:1)

When, simply, Δfb is caused by the overall error of the lens group, itis found that the error of the distance between lenses of the twin-focusadjustment is decreased. Further, it is also found that the effect isincreased in the wide range in which the sensitivity for errors is low,and that disadvantages of the FC adjustment are improved. Further, asshown in Example 7, when AFC and Δff occur simultaneously, thetwin-focus type adjustment has the same effect as that in the zoom lensin which the conventional FC and ff adjustments are conducted.

Next, a region is checked in which the focal length error of thetwin-focus type adjustment is smaller than that of the FC adjustment.

The error Δd after the FC adjustment is:

    Δd=ΔFC-(ΔFC×G+Δff)/G=-Δff/G4

The error Δd after the twin-focus adjustment is:

    Δd=ΔFC-(ΔFC×G+Δff)/(G+1)=(ΔFC-Δff)/(G+1)                                                    5

A region, in which the error of the twin-focus adjustment is smallerthan that of the FC adjustment, is:

In the case of ΔFC/Δff >0 ;

    ______________________________________                                           Δff/G > (ΔFC - Δff)/(G+1)                                                       6                                                         (G+1)/G > (ΔFC - Δff)/Δff                                   (G+1)/G > ΔFC/Δff - 1                                             (G+1)/G + 1 > ΔFC/Δff                                             (2 × G + 1)/G > ΔFC/Δff                                  ______________________________________                                    

In the case of G=2.16 (wide) 2.46

In the case of G=7.79 (telescopic) 2.13

In the case of ΔFC/Δff <0

    ______________________________________                                           -Δff/G > (ΔFC - Δff)/(G +1)                                                     7                                                         -Δff × (G +1) > (ΔFC - Δff)× G                  -Δff × G - Δff > ΔFC × G - Δff         × G                                                                          - Δff > ΔFC × G                                             1/G < - ΔFC/Δff                                              ______________________________________                                    

In the case of G=2.16 (wide) -0.46

In the case of G=7.79 (telescopic) -0.128

When equations 6 and 7 are satisfied, the focal length error of thetwin-focus adjustment is smaller than that of the FC adjustment (in thecase where the twin focus ratio FC_(S) :RC_(S) =2:1)

In the case where the focal length error can be significant other thanin the aforementioned region, the focal length error can be correctedwhen the FC adjustment is conducted at the time when an FC lens frame ismounted on an FC sliding frame, as in the present invention. Further, inthis adjustment operation, an optimum ΔFC/Δff ratio can be selected.

(In the case where the movement ratio of FD_(S) :RC_(S) =2:1, theoptimum ratio is 1)

Further, in the present invention, when the helicoid ratio of the insideand outside of the cam barrel is changed, the ratio of FC_(S) :RC_(S)can be changed. Accordingly, the region, in which sufficient focusingeffect is obtained, can be changed.

As described above, it can be noted that problems due to the FC and ffadjustments conducted in the conventional zoom barrel, can be solvedwhen the focal length is adjusted stepwise in the focal positionadjustment of the zoom lens. Further, it can be noted that the FCadjustment is suitable for the adjustment of each focal length, and thatthe FC adjustment can be improved by the present invention.

In the conventional FC adjustment method, since the distance between thefront lens and the diaphragm is changed by the FC adjustment, thediaphragm can not be positioned at an ideal position. Further, it isnecessary that dead space is provided between the front lens and thediaphragm because of the FC adjustment amount. Furthermore, in the ffadjustment, a large adjusting mechanism other than the zoom drivingsystem is required in order to move the overall zoom barrel, and tosupport it.

As described above, since the zoom lens is adjusted for each focallength only by an amount of rotation of the motor (the rotation angle ofthe cam barrel) in the twin-focus type zoom lens barrel, the FC and ffadjustment mechanism can be eliminated, factors of lens positionalerrors due to these mechanism are eliminated, and the rigidity andoperability are improved, and space which are provided for thesemechanism can be greatly reduced. Due to the twin-focus system, not onlythe accuracy of focal position adjustment, the accuracy of parts, andthe operability of the lens barrel are improved, but also the zoom lensbarrel can be made more compact, and the cost can be lowered further.Further, as compared with conventional zoom mechanisms, since the lensbarrel of the present invention is simplified, and has no exclusivefocusing mechanism, the positional error of lens can be drasticallydecreased. Errors of the focal length in the focal position adjustmentcan be compatible with the lens characteristics and the system of thecamera when the movement ratio of the FC and RC are changed.

The improvement of the lens performance when protruded!

Next, the influence of the twin-focus system on the lens performancewill be described below.

Initially, the influence on the lens performance when the zoom lens isprotruded, is compared with each focusing system. The overall protrusionsystem is adopted by a single focal point lens camera in many cases. Thefront lens focusing system is adopted by a telephoto type two-group zoomlens in many cases. The twin-focus system, according to the presentinvention, and the foregoing two systems are compared with each other,when these three systems are adopted into the telephoto type two-groupzoom lens, in the following table.

                  TABLE 1                                                         ______________________________________                                                  Overall  Front lens Present                                                   protrusion                                                                             focusing   invention                                       ______________________________________                                        Amount of   different for                                                                            constant for                                                                             different                                   protrusion  each focal each focal for each                                                length     length     focal length                                Front lens  large      small      middle                                      movement amount                                                               Angle of view                                                                             narrow     slightly   slightly                                                           broader    narrower                                    Image plane dark       slightly   slightly                                    illuminance            brighter   darker                                      Amount of   increased  decreased  middle                                      peripheral light                                                              Distortion  good       no good    middle                                      ______________________________________                                    

Note:

(1) In the case of the twin-focus ratio FD_(S) :RC_(S) =2:1

(2) When the focusing control is conducted by the overall protrusion inthe telescopic range of the zoom lens, the focusing movement amount ismore than 10 mm in the case where the photographic distance is 0.6 m atthe focal length of 70 mm, and the overall length of the lens barrelbecomes excessively long, which is incompatible with compactness.

As described above, in the present invention, the all characteristicsare desirable except that the protrusion amount is different for eachfocal length.

When the step zoom lens barrel is provided, since there are severaldriving portions for focusing, the difference of the mechanicalprotrusion is generated for each focal length. Accordingly, thecharacteristic, in which the protrusion amount is constant at everyfocal length in the conventional zoom lens, has no meaning in the caseof the step zoom lens barrel.

In the mechanism which was previously explained in the presentinvention, since the distance between the front lens and the diaphragmis not changed when the lenses are protruded, the phenomena does notoccur in which the peripheral light flux, generated at the time of thelens protrusion, is cut.

At the time of the lens protrusion, the small change of the angle ofview is advantageous in the field ratio of the view finder. When theilluminance of the image surface is approximately constant, thedifference of the exposure due to the lens protrusion is smaller. Whenthe deterioration of the image due to the lens protrusion is improved,the closest object distance, at which photographing can be carried out,can be set at a nearer position, which is desirable for use of thecamera.

It is found that the influence on the lens performance at the time ofthe lens protrusion can be improved by the twin-focus system.

The equation by which the effect of the twin-focus is explained!

1. Sensitivity for errors

    G=Δfb/Δd=(f/f1).sup.2

Where,

G: sensitivity for errors

Δd: the changed amount of the distance between lenses

Δfb: the changed amount of the focal position

f1: the focal length of the first lens group (FC lens group)

f: the synthetic focal length (the focal length of the zoom lens system)

Note: A value of the sensitivity for errors is larger as the focallength of the first lens group becomes shorter, and the value of thesensitivity for errors is larger as the synthetic focal length islonger.

It is defined that the movement in the direction of the object is the`positive` direction.

2: The changed amount of the focal position

    Δfb=(FC.sub.S -RC.sub.S)×G+RC.sub.S

Where,

Δfb: the movement amount of the focal point

FC_(S) : the movement amount of the FC lens

RC_(S) : the movement amount of the RC lens

Note: When the movement amount of the RC lens is increased, the movementamount of the FC lens is also increased.

3. The synthetic focal length

    1/f=(1/f1)+(1/f2)-{H/(f1·f2)}

Where,

H: the distance between principal points between the first lens groupand the second lens group

f1: the focal length of the first lens group (FC lens group)

f2: the focal length of the second lens group (RC lens group)

Note: When the FC lens (+) is longer, the synthetic focal length is alsolonger.

When the RC lens (-) is longer, the synthetic focal length is shorter.

When the distance between the lenses is longer, the synthetic focallength is shorter.

4. An amount of protrusion (the overall protrusion type)

    x= R-2·f-H-{(R-H)(R-H-4f)}.sup.1/2 !/2

The above equation approximates the following equation.

    x=f.sup.2 /(R-2·f)

Where,

x: an amount of lens protrusion

f: the focal length

R: the object distance

H: the distance between principal points.

Note: When the focal length is longer, the amount of protrusion islarger.

When the object distance is smaller, the amount of protrusion is larger.

5. The amount of protrusion (the FC protrusion type)

When it is considered that the focal point is made to be constant by theFC protrusion, that is, the overall protrusion is carried out by the FCprotrusion,

    x=f1.sup.2 /(R-2·f1) ##EQU1##

Where,

x: the amount of protrusion

f1: the focal length of the FC lens

R: the subject distance

f0: the focal length before protrusion (at the ∞ position)

fx: the focal length after protrusion (at the ∞ position)

6. The maximum angle of view

    θ=tan.sup.-1 {the diagonal length/2/(the focal length+the amount of protrusion)}×2

Note: When the focal length is shorter by the protruded amount, theconstant angle of view can be obtained.

In the zoom lens, when an amount of a change of the focal length at thetime of protrusion is decreased, the constant angle of view can beobtained.

7. Protrusion at the constant angle of view

From the equation of the protrusion amount: X=f² /(R-2·f), the followingequation is obtained.

When the following presuppositions are used:

f0: the focal length before protrusion (at the ∞ position)

fx: the focal length after protrusion (at the ∞ position)

x: a protruded amount of fx

    f0=fx+x,

    fx= (R+2·f0)-{(R+2·f0).sup.2 -4f0R}.sup.1/2 !/2

8. The angle of view when the zoom lens is protruded

The change of the focal length by the protrusion of the FC lens, isobtained from item 5 as follows;

    1/fx=1/f0-f1/{(R-2·f1)×f2}

The focal length at the constant angle of view is obtained from item 7as follows;

    fx= (R+2·f0)-{(R+2·f0).sup.2 -4.f0.R}.sup.1/2 !/2

When numeric values are substituted into the above two equations, thefocal length by the FC protrusion is shorter than the focal length atthe constant angle of view.

f1=24.5 mm

f2=-22.5 mm

the focal length in the wide angle range: 36.03 mm

the focal length in the telescopic angle range: 60.35 mm

When the zoom lens protrusion is carried out by the FC protrusion forthe subject distance of 0.9 m in the wide angle range, and for thesubject distance of 0.6 m in the telescopic range,

the focal length in the case of 0.9 m in the wide angle range is 34.44mm,

the focal length in the case of 0.6 m in the telescopic angle range is60.35 mm.

The focal length, by which the constant angle of view is maintained, is:

34.59 mm in the case of 0.9 m in the wide angle range, and 60.80 mm inthe case of 0.6 m in the telescopic angle range.

Accordingly, when the zoom lens is protruded by the FC protrusion, theangle of view is broader.

(A) the distance of the focal point at the time of the overallprotrusion (the focal length+the amount of protrusion):

37.60 mm in the case of 0.9 m in the wide angle range,

78.67 mm in the case of 0.6 m in the telescopic angle range.

(B) When twin-focusing is conducted under the condition that FC_(S):RC_(S) is 2:1, and the following values are substituted into theequation of the amount of change of the focal point and the equation oftwin-focus ratio:

the distance of the principal point in the wide angle range=18.28 mm,

the distance of the principal point in the telescopic angle range=11.03mm,

the sensitivity for errors in the wide angle range of 2.16 times,

the sensitivity for errors in the telescopic angle range of 7.79 times,then the following results are obtained:

    Δfb=(FC.sub.S -RC.sub.S)×G+RC.sub.S

    FC.sub.S -RC.sub.S =RC.sub.S

the difference between lenses=G/(G+1).

When the FC protrusion amount is changed to the amount of 2.16/3.16 inthe wide angle range, and to the amount of 7.79/8.79 in the telescopicangle range, and when the second term of the right hand side of thefollowing equation expresses the above ratios;

    1/fx=1/f0-f1/{(R-2·f1)×f2},

then, the following results are obtained;

the focal length for 0.9 m in the wide angle range is 34.93 mm;

and the focal length for 0.6 m in the telescopic angle range is 61.19mm.

Due to the foregoing, it can be found that the change of angle of viewat the time of the protrusion by the twin-focus system with 2 versus 1,becomes slightly narrower. In the present invention, the method, bywhich the angle of view becomes slightly narrower, is adoptedconsidering the amount of the peripheral light and the aberration ofdistortion.

9. Details of the image

The amount of the peripheral light

    Eθ=E0×(Sθ/S0)×(cos θ).sup.4

Where,

θ: the angle of incidence

E0: the illumination on the optical axis

Eθ: the illumination of the focal point corresponding to the angle ofincidence θ

S0: the area of the diaphragm in the front view of the lens

Sθ: the area of the diaphragm viewed from the direction of θ

Due to the foregoing, the broader the angle of view is, the lower theamount of the peripheral light is. Further, in the zoom lens, since theeffective aperture of the lens is determined by a flux of light at the ∞position of the wide angle end, the flux of peripheral light isprevented by the lens frame or the like when the angle of view isbroadened.

Aberration of distortion

Generally, the aberration of distortion of the wide angle lens tends toincrease. In the zoom lens, the wider the angle of view of the zoom lensis, the more distortion aberration is increased, in many cases.

When the angle of view becomes broader by the lens protrusion, theaberration of distortion is increased.

Structure!

Referring to FIGS. 1 to 4, the structure of the present invention willbe described in detail.

FIG. 1 is an exploded perspective view of the zoom lens barrel accordingto the present invention. FIG. 2 is a cross sectional view of the zoomlens barrel. In FIG. 2, the focal point is set in the wide angle rangein the upper half of the zoom lens barrel, and the focal point is set inthe telescopic angle range in the lower half of the zoom lens barrel.FIG. 3 is an illustration showing assembly of the fixed plate. FIG. 4 isa zooming diagram of the zoom lens.

Numeral 1 is a fixed barrel which is integrally fixed to the camerabody, and a female helicoid la is provided on the inner periphery of thefixed barrel. Guide slots 1b for a straight guide 21, which will bedescribed later, are provided across the female helicoid 1a at the leftand right portions of the female helicoid 1a. Numeral 2 is a cam barrel.A male helicoid 2a, which is screwed on the female helicoid 1a, isintegrally formed with a large gear 2b on the outer periphery of the cambarrel. Further, a female helicoid 2c and a cam groove 2d (inner cam)are provided on the inner periphery of the cam barrel 2, and a rib 2e isprovided at the back edge portion in the cam barrel in the directiontoward the inside of the camera. A tip circle of the large gear 2b isformed which is smaller than a minor diameter of the male helicoid 2a,which contributes to down-sizing of the lens barrel. In the case wherethe cam barrel 2 is integrally molded with the large gear 2b, when thelarge gear 2b is positioned on the back end surface of the cam barrel 2,molding can be carried out by a single-unit type mold in the directionof travel, without splitting the forming mold, so that highly accurateparts can be produced by a simple structured mold. Numeral 3 is an FCsliding frame, and an FC lens mirror frame 4, holding an FC lens 5, inwhich the synthetic focal length is (+), is fixed to the FC slidingframe from the front with screws. The dimensional error of productionfor parts of the lens system is adjusted when the screw positions arechanged. Basically, this position adjustment is the same as the FCadjustment. However, it is not necessary that the FC adjustment, whichis used for the individual adjustment, is carried out. A male helicoid3a, which is screwed on the female helicoid 2c, and a guide slot 3b forthe straight guide 21, which will be described later, are provided onthe outer periphery of the FC sliding frame 3, and a hole 3c for a guideshaft 11, which will be described later, is also provided thereon.Numeral 6 is an RC sliding frame, which holds an RC lens 7 by the innerperiphery of the sliding frame. The synthetic focal length of the RClens 7 is (-). On the outer periphery of the sliding frame, a guide slot6a for the straight guide 21 is provided, and an RC cam pin 8, which isengaged with the cam groove 2d, is also provided. A guide shaft 11protrudes from the outer periphery of the sliding frame 6. Numeral 13 isa shaft spring which is inserted into the guide shaft 11. Numeral 12 isan E-ring to prevent a shaft spring 13 from coming off the shaft.Numeral 21 is a straight guide, protrusions 21a of which slide in theguide slots 1b of the fixed barrel 1. Protrusions 21a protrude from theleft and right sides of the straight guide 21. A driving gear 44, whichwill be described later, is rotatably supported by another protrusion21b. Arm portions 21c, which are bent in the forward direction, slide inguide slots 3b and guide slots 6a. Numeral 22 is a guiding fixed-plate,by which the cam barrel 2 is connected to the straight guide 21. Numeral23 is a guiding fixed-shaft by which the straight guide 21 is connectedwith the guiding fixed-plate 22, and the cam barrel 2 is held at a rib2e. Numeral 24 is a set screw by which the straight guide 21 is fixed tothe guiding fixed-shaft 23. Numeral 31 is a barrel driving motor. Apropeller 33 for LDP1, which will be described later, is mounted on ashaft 32 of the motor. The propeller 33 is used for generating a signalLDP1 by a photointerrupter 34 for LDP1. Numeral 35 is a pinion which isdirectly connected to the motor. The rotation of the motor 31 istransmitted to the fifth gear 43, the shape of which is long in thedirection of the optical axis, through the first gear 36, the secondgear 37, the third gear 38 and the fourth gear 42, and furthertransmitted to a driving gear 44. The driving gear 44 is engaged withthe large gear 2b of the cam barrel 2. A propeller 40 for LDP1 ismounted on a shaft 39 of the third gear 38, and generates a signal LDP2by a photointerrupter 41 for LDP2.

Numeral 52 is a shutter, and numeral 53 is a shutter driving motor,which are mounted on the FC sliding frame 3. Numeral 51 is an FPC board,through which the shutter driving motor 53 is connected to a printedcircuit board 54 on which electric components of the main body aremounted. After the FPC board 51 is connected to the shutter drivingmotor 53, the FPC board 51 passes through a gap formed between the armportion 21c of the straight guide 21 and the inner periphery of the cambarrel 2 in the backward direction of the camera. Then, the direction ofthe advance of the FPC board 51 is changed to the forward direction ofthe camera, and the FPC board 51 passes through a gap formed between theouter periphery of the cam barrel 2 and the fixed barrel 1. A hole 1c isprovided in the fixed barrel 1 in the front direction of the camera atthe back end 2f of the cam barrel 2, at which the cam barrel 2 isprotruded to the maximum. The FPC board 51 passes through the hole 1c,and is withdrawn on the outer periphery of the fixed barrel 1. The FPCbarrel 51 is connected to the printed circuit board 54 of the main body.In this context, numeral 51a shows the FPC board 51 at the position inwhich the lens barrel is most retracted. Numeral 61 is the outer shapeof the camera. A decorative ring 62 is mounted on the cam barrel 2, anda front barrel 63 is mounted on the FC sliding frame 3.

Next, basic operations of the zoom lens barrel will be described.

Initially, when the driving motor 31 is rotated, the driving force ofthe motor is transmitted through a gear train 36, 37, 38, and 42 to thefifth gear 43. The driving force is transmitted through the fifth gear43 to the driving gear 44 which is mounted on the straight guide 21. Thedriving gear 44 is engaged with the large gear 2b, and rotates the cambarrel 2. The driving gear 44 moves the cam barrel 2, which ishelicoidally engaged with the fixed barrel 1, in the direction of theoptical axis. At this time, the cam barrel 2 moves forward or backwardin the direction of the optical axis depending on the rotationaldirection of the driving motor 31. The straight guide 21 is integrallyprovided with the rib 2e of the cam barrel 2 by the guiding fixed-plate22, the guiding fixed-shaft 23, and the screw 24. The rotation of thestraight guide 21 is interrupted by the left and right protrusions 21aand the guide slot 1b of the fixed barrel 1. The straight guide 21 onlymoves in the direction of the optical axis. In the same way as theforegoing, the rotation of the FC sliding frame 3 is interrupted at theguide slot 3b by the straight guide 21. Further, since the guide shaft11 protruding from the RC sliding frame 6 passes through the FC slidingframe 3, the rotation of both the RC sliding frame 6 and the FC slidingframe 3 are interrupted. Accordingly, when the cam barrel 2 is rotatedand moved, the FC sliding frame 3, which is helicoidally connected tothe cam barrel 2, and the RC sliding frame 6, which is cam-connected tothe cam barrel 2, are only moved forward or backward in the direction ofthe optical axis. The FC sliding frame 3 moves at a ratio of 2 times ofthe distance which the cam barrel moves. This ratio is determined byleads of the inner helicoid and the outer helicoid of the cam barrel. Inthis embodiment, since approximately the same leads are provided, themovement ratio is the above described ratio. The engaged position of thefifth gear 43 with the driving gear 44 is changed in the direction ofthe optical axis accompanied with the movement of the cam barrel 2.However, since the fifth gear 43 is an elongated gear in which longteeth are provided in the direction of the optical axis, the engagementof the gears is always maintained, in spite of the movement of the cambarrel. The rib 2e of the cam barrel 2 is provided to prevent thestraight guide 21 from being disengaged from this assembly. The innersurface of the rib 2e forms a bearing surface by which the rotation ofthe cam barrel is supported, and prevents the cam barrel 2 from beingdeformed at the time of driving force transmission.

The RC sliding frame 6 holding the RC lens 7, is driven by the camgroove 2d as described above, and the shape of the cam is divided intotwo regions, a focusing region and a focal length switching region, sothat the focusing operation and the focal length switching operation canbe carried out by the same driving means. In this embodiment, 5 focallengths are selected as shown in FIGS. 3(A) and 3(B). However, in orderto have an adjustment margin in the focusing operation, the shape ofcams in the focusing region are respectively set in the manner that thecam shapes are longer than the distance from the theoretically infiniteposition to the closest distance position. Although the relativedistance of the RC sliding frame 6 to the cam barrel 2 is not changed inthe focusing region and the retractable operation region, (the RCsliding frame 6 moves at approximately 1/2 of the ratio of the FC lens5, when viewed from the focal plane), the RC sliding frame 6 has aninclination characteristic in which the RC sliding frame moves at ahigher ratio than the FC lens 5 in the zooming region when viewed fromthe focal plane. The FC lens 5 always moves linearly with respect to therotation of the motor. The RC lens 7 moves linearly with respect to therotation angle of the motor 31 in both the focusing region and the focallength switching region, however, the inclination characteristic of theRC lens 7 is different depending on each region. The shape of theconnecting portion of the cam portion, by which the focusing region isconnected to the focal length switching region, is nonlinear, that is,arc-shaped. Accordingly, the operability of the RC lens 7 is increased,and it is difficult to add the force in the radial direction to the RClens 7. The inclination characteristics of 4 focal length switchingregions between focusing regions are not the same. The relative movementof the lenses is described as follows: when focusing is conducted at anear distance, being switched from the infinite distance, the FC lens 5and the RC lens 7 are separated from each other and both are separatedfrom the focal plane; and when the focal length is switched from thewide angle range to the telescopic angle range, the FC lens 5 and the RClens 7 approach each other, and are separated from the focal plane.

The guide shaft 11 protruded from the RC sliding frame 6 penetrates theFC sliding frame 3, and the compressed shaft spring 13 is held by theE-ring at the front end of the guide shaft 11. Accordingly, the RCsliding frame 6 is always pulled in the direction of the FC slidingframe 3 by the spring force. Therefore, only one surface of the cam ofthe cam groove 2d of the cam barrel 2 is used. Accordingly, the width ofthe cam groove is larger than that of the cam pin, and is sufficient forthe operation of the cam pin. A rise angle of the cam groove isasymmetrical at the nearest side and at the opposite side in the mannerthat the rise angle of the cam groove is increased as large as possibleat the nearest side so that the operational efficiency of the cam grooveis increased. Plastic molding of this cam can be easily carried out.When the focusing operation is carried out, the RC sliding frame 6 ismoved in the direction in which the spring force applied to the RCsliding frame is increased. When the focal length is switched, the RCsliding frame 6 is moved in the direction in which the spring forceapplied to the RC sliding frame is decreased. The cam groove 2d isopened in the forward direction of the optical axis. When the RC slidingframe 6 is assembled into the cam barrel 2, it is assembled from thefront of the cam barrel 2. This RC sliding frame 6 is connected to theFC sliding frame 3 (including the shutter 52 and the like) by the guideshaft 11. Accordingly, the FC, and RC sliding frames are assembled intothe cam groove in a unit. In this case, when the RC sliding frame 6 ispulled to the FC sliding frame 3 side, the good assembling operabilityis obtained.

Normally, the lens performance, such as the resolving power forprojection, is checked at the inspection step of the cam barrel unitincluding FC and RC sliding frame unit. However, when the cam barrelprovided on the outer surface of the cam barrel unit is rotated, boththe focal length selection and the focal position adjustment can becarried out, so that the efficiency of the inspection is very high, andlarge electric tools are not necessary. When the lens performance, suchas the resolving power for projection, is inspected under thiscondition, defects can be easily detected, and the overhaul/repair timeand cost can be greatly reduced. It is not necessary that the shutterdriving portion, FPC, and lens cover are assembled in this unit, andfurther the focusing mechanism need not be assembled in this unit.Accordingly, replacement of a defective FC lens can be easily carriedout.

After the cam barrel unit has been housed in the fixed barrel 1, thestraight guide 21 is installed, and the two fixed plates 22 to supportthe straight guide 21 are installed. These assembling operations areexplained below, referring to FIGS. 3(A) and 3(B). In FIG. 3(A), inorder to increase the assembling operability, two temporary fixed plates22 are fixed to the straight guide 21 respectively by screws 24. Afterthe straight guide 21 has been installed in the cam barrel 2 from theback of the camera, the two fixed plates 22 are rotated clockwise aroundthe screws 24, and screwed onto the straight guide 21 at 6 positions bythe screws 24 and screws 25, as shown in FIG. 3(B). As described above,the straight guide 21 can linearly guide the fixed barrel 1 and the FCsliding frame 3 by a single part. Accordingly, the FC sliding frame 3can be very accurately moved linearly, and resulting in high efficiencyof the driving force for the linear movement.

The cam barrel 2 is synchronously moved with the straight guide 21 inthe direction of the optical axis. A driving gear 44 is mounted on thestraight guide 21. Accordingly, even when the cam barrel 2 moves in thedirection of the optical axis, the position in the direction of theoptical axis with respect to the driving gear is not changed. Therefore,the shape of the large gear 2b provided on the cam barrel 2 is a simplestructure so that the width of the teeth of the large gear 2b is limitedto a predetermined value, and projects from the back end of the cambarrel. This is done from the reason that the dimension of the largegear in the direction of the optical axis is reduced to be as small aspossible. When the shape of the gear on the cam barrel is helicoidal, orthat gear is replaced by several gears, an intermediate driving gear isnot necessary. This gear, which is long in the direction of the opticalaxis, can reduce the number of gears, however, the length of the gear inthe direction of the optical axis is long on the cam barrel. When thelength of the gear on the cam barrel in the direction of the opticalaxis is long, a large retractable amount of the lens barrel can not beobtained since this gear appears on the exterior of the camera. When therotation angle of the gear is small, the dimension of the gear in thedirection of the optical axis can be smaller. However, since the lensbarrel is moved in the forward direction or rearward direction by asmall rotation angle, the lead of the helicoid, and the lead of the camare extended, so that the backlash in the direction of the optical axisis increased and the focusing accuracy is adversely affected. Further,since the driving force for moving the lens barrel is increased, largedeformation occurs in a plastic lens barrel when the driving force istransmitted. Further, when the gear is replaced by several gears, alarge rotation angle can be obtained. However, in this case, when thesize of the gears are different, not only does transmission loss occur,but also the number of split of the mold is increased even when thegears are integrally plastic-molded. Accordingly, in order to obtain asuitable gear shape, high accuracy and high cost are necessary. When thegear, which is long in the direction of the optical axis, is used fortransmitting the driving force, since the diameter of the root circle ofthe gear of the cam barrel is larger than the diameter of the tip of thehelicoid, the diameter of the gear portion on the cam barrel is largerthan that of the helicoid portion, and its surrounding members, such asthe fixed barrel, become large, then the lens barrel becomescorrespondingly large.

As described above, according to the movable gear system of the presentinvention, a large retractable amount of the lens barrel can beobtained, the rotation angle of the cam barrel is large, and the outerdiameter of the lens barrel can be decreased. Further, when the gearportion is located outside the surface of the back end of the cambarrel, and not only the structure of the mold is simplified, but alsowhen the rib is provided inside the cam barrel, sufficient bottomthickness of the gear can be obtained, and when the rib is so supported,the deformation of the cam barrel at the time of driving forcetransmission can be prevented at every rotational position.

As shown in FIG. 4, three signals, that is, the continuous pulse signalLDP1 in which the rotation of the driving motor 31 is detected by aphotointerrupter 34, the intermittent pulse LDP2 in which the rotationof the third gear in the gear train is detected by the photointerrupter41, and the SPOS in which the position of the end of the retracted lensbarrel is detected by a switch, not shown in the drawing, are used forthe drive control. The focal length is divided in the manner that thedifference of the distance between the ∞ focal position in the wideangle range and the ∞ focal position in the telescopic angle range, isdivided into an integer (4-division). This is due to the reason that thefocal length is controlled by the periodically generated signal LDP2,and the reason why a method, in which the LDP2 is generated by theperiodical rotation mechanism, is small and of low cost, and further themethod can be carried out without contact, as the method by which thefocal length is selected for a predetermined rotation amount of themotor.

In other words, the intervals of the positions of the FC lens at thefocal positions of the wide ∞, middle ∞, middle 2 ∞, middle 3 ∞, andtele ∞, are equal, and the rotation amount of the motor is the same.When the difference between the above-described positions is small, itis not necessary that the distance is equal. However, since the amountof an approach of the focusing operation is the same for each focallength, an inefficient focus time is prevented for each focal length.Further, setting of the allowable focal position adjustment amount iseffective for each focal length.

The LDP2 for the focal length control is used as a trigger pulse whenthe count of the lens protruding pulses at the time of focusing isstarted. When the generation time of the LDP2 is mechanically changed,the focal position adjustment can be carried out. Specifically, when thepropeller 40 for LDP2, the axle of which is lightly press-fit in theshaft 39 of the third gear 38, is slipped in the direction of therotation, the position of generation of the LDP2 is changed. The spacefor adjustment is not necessary when the position of the propeller,which periodically generates the pulses, is changed. Accordingly, thefocal position adjustment can be carried out without taking upadditional space. This adjustment is carried out as the general focalposition adjustment operation of the lens barrel unit before it ismounted to the main body, and the wide angle end with low sensitivityfor error is adjusted at the ∞ focal length. After that, in the completeunit of the camera, the focal position adjustment is carried out foreach focal length, and the deviation from the general adjustment, andthe deviation for each focal length are stored in the EEP-ROM. The focalposition adjustment is carried out when the generation time of the LDP2is changed, or when pulses to be counted are corrected by a triggersignal. In both cases, the focal position adjustment is carried out bythe rotation angle of the cam barrel.

Further, the LDP2 is also used as a trigger signal for the start of thestop control at the time of the focal length selection. Approximately 23pulses are included in the width of the Hi-level of the LDP2, which isset in the manner that the number of pulses equals the total of thepulses, which are necessary in the case where the motor is controlledfor stopping at the side of lens barrel protrusion, and pulses, whichare necessary in the case where the motor is controlled for stopping atthe side of lens barrel which is retracted. That is, the pulse width ofLDP2=the width of ZOOM-UP stop pulses+the width of ZOOM-DOWN stoppulses.

According to this setting, even when the lens barrel stops from eitherdirection, the lens barrel stops without fail at the position where LDP2is Hi. Further, even when the lens barrel stops from either direction,the lens barrel stops at approximately the same position.

Also, when the zooming operation is carried out by pressing a buttonwhich is provided outside the camera, it is estimated when the LDP2rises whether or not the control is shifted to the zoom stop control (atthe time of ZOOM-DOWN, it is estimated when the LDP2 falls).Accordingly, since the estimation is carried out only when the LDP2rises and is changed, the zoom button Sw, in which much chatteringoccurs, can be used. Further, even when the Sw is intermittentlyoperated, the lens barrel can be correctly operated.

The zooming operation is carried out under the condition that the lensbarrel stops at a specified position, in which the LDP2 is Hi, at everyfocal length when photographing is carried out. Accordingly, when theLDP2 is not Hi at the start of the focusing operation, it is judged thatthe lens barrel is erroneously operated from the outside (the cam barrelis manually rotated), and the lens barrel is moved to the initialposition for initializing (SPOS signal).

Functions of the LDP2 are arranged as follows.

1 The position control at the time of focal length selection (therelative number of pulses from the initial position)

2 The stop control trigger signal at the time of focal length selectionby the outside operation.

3 The protrusion count trigger signal at the time of focus control.

4 The stop control trigger signal at the time of position return controlafter focus control.

5 The outside erroneous operation detection function.

6 The focal position adjustment function.

Conventionally, in a camera with a zoom lens, in order to increase thefocusing performance, the zooming operation is carried out in the mannerthat the operation is completed under the normal rotation drivingcondition at the time of reverse rotation control even in the lensbarrel which has backlash at the time of zooming control. In such acase, looseness of the mechanism is absorbed under the normal rotationdriving condition. However, when the zooming operation is completed, andthe lens barrel is touched by hand, looseness, which has been absorbed,is removed. After that, when the photographing operation is carried outwithout touching the zoom lens, the focal position is adversely changed.

In the present invention, the driving section for the change of thefocal length and the driving section for the focusing operation arecomposed of the same mechanism. Accordingly, when the focusing operationis controlled by the normal rotation, the backlash at the time ofzooming operation is finally eliminated at the time of focusingoperation even when looseness is removed by the outside operation, oreven when the lens barrel is intentionally moved forward or backward.Therefore, backlash absorption control of the lens barrel is notnecessary, and stable focusing performance can be obtained.

The initial position control of the lens barrel is carried out by thetime control after the rise of the SPOS. The driving motor is reversedand a current flows until the SPOS is lowered. After the SPOS has beenlowered, the above-described condition is maintained for a predeterminedtime, and then the driving motor is stopped. This predetermined time canbe changed for the purpose of adjusting the individual difference of theretracted lens position. Although time is used for controlling thepredetermined amount, pulses (LDP1) generated from the motor may beused.

When the main switch of the camera is ON, it is checked whether the SPOSis Hi. Then, after 5 rising portions of LDP2, the stop control operationis conducted, and preparation for wide range photography is completed.When the SPOS is low at the time of the start of the control, the lensbarrel is initialized and the same processing is carried out.

The cam groove 3b provided on the cam barrel 2, according to the presentinvention, is parallel (at right angles with the optical axis) with thedirection of rotation of the cam barrel in the focusing range, and thistype cam is called a horizontal cam. The horizontal cam is provided forthe following reasons.

In the case of the step zoom, a portion, which is actually used at thetime of photography, is only in the focusing region. Accordingly, it issufficient that good focusing accuracy is maintained only in thisportion, and in the focal length change portion, only the zoomingfunction is necessary. Accordingly, the horizontal cam is advantageousin that the focusing accuracy is retained in the focusing region. The RCsliding frame 6 is engaged with the cam and slid in the groove, and someplay is necessary for the RC sliding frame in order to ensureoperability. In this case, the play is generated in the direction of therotation. In the case where play is provided in the direction of therotation, when the engaging cam is inclined, the RC sliding frame 6 ismoved in the direction of the optical axis due to this play, whichinfluences the focusing accuracy. In play in the direction of rotationof the RC sliding frame 6, the influence of the horizontal cam on thefocusing accuracy is the least. There are individual differences in theshape and dimensions of parts provided around the RC sliding frame 6.Even when there is individual difference in the direction of therotation in the above-described individual differences, if thehorizontal cam is used, only the position, at which the cam is used, ischanged, and positional error of the lens does not occur. That is,finally, the generation of the focal length error is improved. When thecam is inclined, the periphery of the RC sliding frame 6 is deformedwhen the power is transmitted to the cam. Since the lens is changed inthe direction of the optical axis due to the deformation, the focusingaccuracy is lowered due to the dispersion of the amount of deformation.In order to improve this lowering of the focusing accuracy, the rigidityof the RC sliding frame 6 is increased, however, this results in largersize and higher cost of the zooming mechanism. Especially, when the camis made of plastic, the horizontal cam is adequate. The RC sliding frame6 is engaged with the cam groove 2d by the RC cam pin 8. When thesliding frame does not move smoothly, abrasion in addition todeformation of the sliding portion occurs. In order to prevent theabrasion, the driving load of the cam inclination, and the pressure onthe sliding surface are decreased. The horizontal cam is sufficient forthe above-described operations. The cam barrel 2 is integrally molded ofplastic, and the horizontal cam shape is very stable. Since the cam ishorizontally formed, FC_(S) :RC_(S) has the characteristic of 2:1(FC_(S) :the amount of movement of the FC lens, RC_(S) :the amount ofmovement of the RC lens), that is, this ratio is determined by the ratioof the leads of two helicoids. This is due to the following reasons: inorder to decrease the total length of the lens barrel by the doublehelicoids when the lens barrel is collapsed, the retracting efficiencyof the lens barrel is high when the ratio of the leads of the helicoidsis 1:1; further, when the shutter and FPC are installed in the lensbarrel, it is preferable that the leads of the helicoids are the same.Accordingly, the ratio of the movement of the FC sliding frame 3 and thecam barrel 2 is preferably 2:1 for mechanical reasons. Further, for theamount of the focusing movement and the focal position adjustmentproperty in the telescopic angle range, and improvement of the lensperformance in the wide angle range, it is preferable that the ratio ofFC_(S) and RC_(S) is 2:1 even in the twin-focus system. Due to theforegoing reasons, the horizontal cam is preferable in the focusingregion.

In this embodiment, the movement diagram of the FC lens 5 by thehelicoid, and the movement amount of the RC lens 7 by the cam is shownin FIG. 4. Since, the RC lens 7 is moved by the horizontal cam in arange of ∞ to 0.8 m (0.6 m) in the focusing region, the movement ratioof the RC lens 7 is lower than that of the FC lens 5. Further, althoughthe focal length switching is conducted in the range of 0.8 m to ∞,since the FC lens 5 is formed into a convex lens and the RC lens 7 isformed into a concave lens, the movement ratio of the RC lens 7 ishigher than that of the FC lens 5, due to the characteristic of the zoomlens. In every focusing region, the operation region of the horizontalcam is wider than the space from the infinite position to the closestposition (0.8 m), and the focal position can be sufficiently adjustedfor each camera or each focal length.

Due to the foregoing reasons, when the shape of the cam in the focusingregion is formed in the same direction as that of the rotation(horizontal cam), it can be seen that the horizontal cam is advantageousfor accuracy, down-sizing, and cost.

In order to maintain the horizontal position of the cam and in order toaccomplish the twin-focus system, it is advantageous that a member, inwhich the cam is set, is moved in the direction of the optical axis.Accordingly, the cam is set inside the rotating and moving barrel (cambarrel). When the horizontal cam is set at a portion which is located atan equal distance from the sliding frame 3, the whole lens barrel isprotruded in the focusing operation. When the horizontal cam is set at aportion which is located at an equal distance from the fixed barrel 1,the focusing operation is carried out by the front lens focusing.

Further, it is not necessary that the ratio of the protrusion of the FClens and RC lens is the same for each focal length. That is, in order todecrease the sensitivity for error in the telescopic angle range, theamount of the movement of the RC lens is sometimes increased. Inversely,in order to decrease the amount of the movement of the FC lens, theamount of the movement of the RC lens is decreased. Further, in order toincrease the lens performance of the wide angle lens, the amount of themovement of the RC lens is increased. That is, the most preferablesystem for the camera may be selected.

Considering the adjustment of the individual focal position difference,it is convenient that cams are linear, however the cams are not limitedto being linear. It is not always necessary that the direction of themovement of the RC lens is the same as that of the FC lens. Further, theamount of the movement of the RC lens may be larger than that of the FClens.

In the present invention, the following variation can be considered.That is, in FIG. 4, in the range in which the focal length switchingoperation is carried out, the sharpest inclination is between the wideportion (W) and M1, and the cam inclination is sharp. This is the reasonwhy the inclination of the track of the RC lens is sharper in the wideangle range than in the telescopic angle range, in the case where thetrack of movement of the FC lens is made linear. The inclination of thecam is the sharpest in the range between the wide portion and M1 whenthe movement amount of the FC lens is divided into equal portions. Whenthe inclination is so sharp as described above, since the load fordriving the lens barrel is increased, normally, the rotation angle ofthe cam barrel is enlarged, and the inclination angle of the cam islowered to less than 45°. However, when the rotation angle of the cambarrel is enlarged, time for switching the focal length and for focusingis increased, or a sufficient gear ratio for the driving portion can notbe obtained. Here, when the closest distance for photography in the wideangle range is limited, the inclination can be allowed to be slightlylowered. Normally, in a zoom lens, when close distance photography iscarried out in the telescopic angle range in which magnification islarge, the closest distance photography is not always necessary in thewide angle range. Further, in order to carry out the close distancephotography in the wide angle range, the load on the lens design islarge. Further, in the case of the telephoto type 2-group zoom, sincethe protrusion amount of the zoom lens is different for each focallength in the focusing system except the front lens focus system, thesame driving control is not always conducted for each focal length. Inthe zoom lens barrel which has an independent focusing region for eachfocal length as described above, when the appropriate closest distanceis set for each focal length, considering the cam portion of the drivingsystem and the lens design, a high efficiency mechanism, and adown-sized and lower cost photographing lens can be supplied.

Although a 2-group zoom lens is described above, also in a multi-groupzoom lens, not less than 3-groups, the same effect can be obtained whenmore than 2-group lenses, in the lenses used for magnification, are usedfor focusing and focal position adjustment. Naturally, in the case ofmulti-group zoom lenses, it is considered that the above-describedoperations are conducted with the overall protrusion operation, thefront lens focusing operation, the rear focusing operation, or the innerfocusing operation. When the case where a single-lens group is moved, iscompared with the case where other magnification lenses are also movedwith the single-lens group, the following effects can be obtained:

1. the movement ratio between two-group lenses is different, and theamount of movement of the original focus lens groups is changed;

2. the focal position adjustment is carried out for each focal length,and effects of the adjustment of the distance between the lens groups,and effects of the adjustment of the overall lens groups can be obtainedwhen focal position adjustment is carried out; and

3. the synthetic focal length (angle of view) is changed when comparedwith that in the case of the single protrusion of the original focuslens groups.

When the above-described effects simultaneously occur, all the effectsare also included in the present invention.

According to the present invention, when the RC lens, in addition to theFC lens, is moved at the time of focusing, a high resolving power of thefocus control can be obtained, the influence of the error of the stopposition over the accuracy of the focal position can be decreased, andthe focal position adjustment mechanism can be simplified. Further,since the lens performance in the protrusion mode can be improved, ahigh performance, down-sized, and low cost lens can be provided. As awhole, because of a high focusing performance, reasonable focal positionadjustment, and improvement of the lens performance and the like, a highperformance, small, and low cost zoom lens barrel can be accomplished.

What is claimed is:
 1. A zoom lens barrel comprising:a zoom lensincluding a first lens group and a second lens group located fartherfrom an object than said first lens group; a first lens frame forholding said first lens group therein; a second lens frame for holdingsaid second lens group therein; a cam barrel having a helicoid forengaging said first lens frame; a first cam groove disposed on said cambarrel; a second cam groove disposed on said cam barrel; a cam pin,disposed on said second lens frame, for engaging said first and secondcam grooves, wherein said cam pin engages said first cam groove while afocusing operation is conducted and said cam pin engages said second camgroove while a focal length switching operation is conducted; and amoving mechanism for moving said first and second lens groups, whereinsaid moving mechanism stepwise switches focal length of said zoom lensby moving said first and second lens groups, said moving mechanismadjusting a focal point of said zoom lens by moving said first andsecond lens groups while changing a gap between said first and secondlens groups after a predetermined focal length is selected.
 2. The zoomlens barrel of claim 1, wherein said moving mechanism rotates said cambarrel so as to move said first and second lens groups.
 3. The zoom lensbarrel of claim 1, wherein said first cam groove is positionedperpendicular to an optical axis of said lens barrel and said second camgroove is positioned at an incline with respect to said optical axis. 4.The zoom lens barrel of claim 1, wherein said first and said second camgrooves communicate with each other.
 5. The zoom lens barrel of claim 1,wherein said first lens group has a convex lens and said second lensgroup has a concave lens.
 6. The zoom lens barrel of claim 1, whereinsaid moving mechanism adjusts said focal point of said zoom lens bymoving said first and second lens groups relative to said cam barrel. 7.A zoom lens barrel comprising:a zoom lens including a first lens groupand a second lens group; a first lens frame for holding said first lensgroup; a second lens frame for holding said second lens group; a cam pindisposed on said second lens frame; a cam barrel having a helicoid forengaging said first lens frame and a cam groove for engaging said campin; and a rotating mechanism for rotating said cam barrel, wherein saidfirst and second lens groups are moved at the same time according to therotation of said cam barrel so as to switch a focal length of said zoomlens stepwise and adjust a focal point of said zoom lens, a gap betweensaid first and second lens groups being changed during the adjustment ofsaid focal point.
 8. The zoom lens barrel of claim 7, wherein said camgroove includes a first cam groove and a second cam groove.
 9. The zoomlens barrel of claim 8, wherein said cam pin engages said first camgroove during the adjustment of said focal point and said cam pinengages said second cam groove during the switching of said focallength.
 10. The zoom lens barrel of claim 9, wherein said first and saidsecond cam grooves communicate with each other.